We may think of them as silent, but fish make many sounds that are rarely appreciated by the human ear. Clownfish chirp and pop by gnashing their teeth together. Oyster toadfish hum and blare like foghorns by quickly contracting muscles attached to their swim bladders. Croaking gourami make their signature noise by snapping the tendons of their pectoral fins. Altogether, more than eight hundred fish species are known to hoot, moan, grunt, groan, thump, bark, or otherwise vocalize.